Three new alkamides, tulipiferamides
A–C (1–3, respectively), and
30 known compounds (4–33) were obtained
from the roots of Liriodendron tulipifera (Magnoliaceae).
Dehydrotemisin (4), an elemane sesquiterpene lactone,
was isolated for the
first time from nature. The structures were deduced by the interpretation
of NMR spectroscopic and MS spectral data. The geometries of the double
bonds in tulipiferamides A–C (1–3, respectively) were determined on the basis of 1H–1H coupling constants and 13C chemical shifts. The
presence of the alkamide type in this plant is reported for the first
time. An analysis of the inflammatory response revealed that seven
compounds (1, 4, 7, 9, 14, 23, and 27) suppressed
the nitric oxide production induced by LPS in RAW264.7 macrophages.
Furthermore, tulipiferamide A (1) inhibits NF-κB
activation by selectively targeting IKKβ, an upstream kinase
of NF-κB, resulting in the suppression of inflammatory mediators,
including iNOS, COX-2, IL-1β, TNFα, and IL-6. Our results
provide a rationale for the further development of tulipiferamide
A as a selective IKKβ inhibitor to modulate inflammatory diseases.